Two tiny Mazon Creek fish enter the LRT

“Elonichthys” peltigerus and “Elonichthys” hypsilepis
(Figs. 1–3) are two tiny palaeoniscid fish found by cracking open small brown concretions in the Mazon Creek Formation, a Middle Pennsylvanian locality not far from Chicago. This site is most famous for producing soft tissue specimens, including the odd flatworm, Tullimonstrom.

Figure 1. The two tiny Elonichthys specimens (at bottom) together with their relatives to scale (smaller than actual size here on a 72 dpi monitor). See figure 2 and 3 for a closer look.

Ontogenetic (= growth) series are known for both taxa.
Both exhibit allometry (= proportional changes during maturation), as in most fish.

Figure 2. “Elonichthys” hypsilepis growth series full scale on 72 dpi monitor and larger.

Other Elonichthys specimens
are found in South Africa, Europe and Greenland in Carboniferous and Permian deposits.

Figure 3. “Elonichthys” peltigerus growth series full scale on 72 dpi monitor and larger.

The type specimen is
Elonichthys gemari (Giebel 1848). The Mazon Creek specimens were studied by Schultze and Bardack 1987 and Schindler 1993.

Figure 4. Subset of the LRT focusing on Elonichthys and their kin.

Here
in the large reptile tree (LRT, 1980+ taxa, subset Fig. 4) both species of the genus Elonichthys nest with Pteronisculus and Boreosomus (Fig. 1). The only living member of this clade is Engraulis, the anchovy.

References
Giebel C 1848. auna der Vorwelt mit steter Berücksichtigung der lebenden Thiere. Monographisch dargestellt 1(3):
Schultze H-P and Bardack D 1987. Diversity and size changes in palaeonisciform fishes (Actinopterygii, Pisces) from the Pennsylvanian Mazon Creek fauna, Illinois, U.S.A. Journal of Vertebrate Paleontology 7:1–23. http://dx.doi.org/10.1080/02724634.1987.10011635
Schindler T 1993. What is Elonichthys GIEBEL? The Gross Symposium and SDS Field Meeting: IGCP 328 Palaeozoic Microvertebrates and Subcommission for Devonian Stratigraphy Joint Meeting At: Göttingen Abstract volume

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